SVM: make nested page-fault tracing and logging consistent

SVM: make nested page-fault tracing and logging consistent

Don't call __get_gfn_type_access() more than once, to make sure data
recorded for xentrace matches up with what gets logged in case of the
domain getting crashed.

As a side effect this also eliminates a type mismatch reported by
Norbert Manthey, as the first call now also needs to update the local
variable "p2mt".

Do a few cosmetics at the same time: Move a comment up a little, drop
the pointless "case 0" (seeing in particular the comment's wording),
and correct formatting.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>